A Triassic averostran-line theropod from Switzerland and the early evolution of dinosaurs

Abstract

Our knowledge of the fossil record of early theropod dinosaurs has greatly improved over the last two decades. Yet still very little is known about European taxa because they are largely incomplete. Here we present an exceptionally well preserved theropod skeleton from the Late Triassic of Europe, pertaining to a new genus and species. The specimen includes a nearly complete skull, two articulated forelimbs, and stomach contents. Notatesseraeraptor frickensis gen. et sp. nov. is an early diverging neotheropod with affinities to Dilophosaurus + Averostra and displays an interesting mixture of character states typically seen either in coelophysids or in dilophosaurids. Based on our phylogenetic analysis N. frickensis gen. et sp. nov. is considered one of the currently oldest and most basal members of the lineage, leading to Averostra. A monophyletic ‘traditional Coelophysoidea’ including Dilophosaurus is not supported.

A comprehensive anatomical and phylogenetic evaluation ofDilophosaurus wetherilli(Dinosauria, Theropoda) with descriptions of new specimens from the Kayenta Formation of northern Arizona

“…Instead, Dilophosaurus wetherilli is supported as a stem-averostran more derived in the direction of Averostra than Cryolophosaurus ellioti and Zupaysaurus rougieri . This result reflects previous hypotheses that recovered taxa that were assigned previously to the Coelophysoidea, such as Dilophosaurus wetherilli , as paraphyletic group more closely related to averostrans (Carrano et al, 2002; Rauhut, 2003; Smith et al, 2007; Langer et al, 2014; Zahner and Brinkmann, 2019). The characters that previously pulled Dilophosaurus wetherilli up the tree into Ceratosauria are found to be either homoplastic or redistributed across the tree, thanks to the discovery of new fossils and reinterpretations.…”

“…37.6). This is similar to the vagus foramen found in Notatesseraeraptor frickensis Zahner and Brinkmann, 2019 and Cryolophosaurus ellioti , but is in contrast to the plesiomorphic condition in which the glossopharyngeal (CN IX), vagus (CN X), and accessory nerves (CN XI) all pass through the metotic fissure (Gower and Weber, 1998; Sampson and Witmer, 2007; Knoll et al, 2012; Lautenschlager and Butler, 2016; Sobral et al, 2016; Lessner and Stocker, 2017; Chapelle and Choiniere, 2018; Paulina-Carabajal et al, 2019; Piechowski et al, 2019). The glossopharyngeal nerve (IX) penetrates the braincase near the top of the fenestra pseudorotunda, slightly anterior to the position in some tetanurans (Paulina-Carabajal and Currie, 2017).…”

“…This hypothesis was also supported in subsequent phylogenetic analyses (Rowe and Gauthier, 1990; Tykoski, 1998, 2005; Holtz, 2000; Tykoski and Rowe, 2004), or as a coelophysoid down-tree from Ceratosauria (Ezcurra and Novas, 2007; Carrano et al, 2012; Xing, 2012). The most recent consensus is that Dilophosaurus is not a member of Coelophysoidea (as defined by Nopsca, 1928; sensu Holtz, 1994) but is pulled crown-ward, so that Dilophosaurus wetherilli and coelophysoids are non-averostran neotheropods (Averostra includes the Ceratosauria and Tetanurae lineages; Carrano et al, 2002; Paul, 2002; Rauhut, 2003; Yates, 2005; Ezcurra and Cuny, 2007; Smith et al, 2007; Hendrickx and Mateus, 2014; Langer et al, 2014; You et al, 2014; Nesbitt and Ezcurra, 2015; Novas et al, 2015; Martill et al, 2016; Ezcurra, 2017; Langer et al, 2017; Zahner and Brinkmann, 2019; Fig. 2.3) along with taxa such as Zupaysaurus rougieri Arcucci and Coria, 2003 (Ezcura and Novas, 2007), Dracovenator regenti Yates, 2005, Cryolophosaurus ellioti Hammer and Hickerson, 1994 (Smith et al, 2007), Tachiraptor admirabilis Langer et al, 2014, and, depending on the phylogeny, Sinosaurus triassicus Young, 1940 (Xing, 2012) and Berberosaurus liassicus Allain et al, 2007 (Xu et al, 2009).…”

“…Outcrop area modified from Cooley et al (1969).

Figure 2.The phylogentic position of Dilophosaurus wetherilli in previous hypotheses using parsimony methods: ( 1 ) as a non-tetanuran theropod (Forster, 1999), ( 2 ) as a coelophysoid ceratosaur (e.g., Rowe and Gauthier, 1990; Holtz, 1994, 2000; Tykoski, 1998, 2005; Tykoski and Rowe, 2004; Ezcurra, 2006; Ezcurra and Cuny, 2007; Ezcurra and Novas, 2007; Carrano et al, 2012; Xing, 2012; Novas et al, 2015), and ( 3 ) as a stem-averostran neotheropod (e.g., Carrano et al, 2002; Rauhut, 2003; Yates, 2005; Smith et al, 2007; Hendrickx and Mateus, 2014; Langer et al, 2014; You et al, 2014; Nesbitt and Ezcurra, 2015; Martill et al, 2016; Ezcurra, 2017; Langer et al, 2017; Zahner and Brinkmann, 2019). The highlighted node in ( 2 ) represents either the most recent common ancestor of all neotheropods or averostrans, depending on the analysis.

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Pendraig milnerae , a new small-sized coelophysoid theropod from the Late Triassic of Wales

“…bonoi : PVSJ 906; Coelophysis sp. : PEFO 21373/UCMP 129618; Notatesseraeraptor frickensis [ 74 ]; M. rhodesiensis : NHMZ QG 1; D. wetherilli [ 64 ]). The dorsal margin of the iliac blade of P. milnerae possesses a somewhat thickened, mostly flat surface that faces slightly laterally.…”